Public Health Notice - Ongoing outbreak of norovirus and gastrointestinal illnesses linked to raw and undercooked oysters from British Columbia

March 7, 2017

This notice has been updated to include information about the ongoing risk of illness and to reflect an additional 22 cases that have been reported in the outbreak. There are now 289 cases of gastrointestinal illnesses under investigation.

Why you should take note

The Public Health Agency of Canada is collaborating with federal and provincial public health partners to investigate norovirus and gastrointestinal illnesses in British Columbia, Alberta and Ontario linked to raw and undercooked oysters. The source of illness has been identified as oysters from British Columbia but the cause of the contamination has not been identified. The outbreak is ongoing with illnesses linked to raw and undercooked oysters continuing to be reported, indicating contaminated oysters remain on the market (including restaurants, seafood markets and grocery stores). There continues to be a risk of norovirus infection and gastrointestinal illness associated with the consumption of these oysters.

Although not all cases of illness have been tested, testing of several cases has confirmed the presence of norovirus infection. It is suspected that norovirus illness, caused by consumption of contaminated oysters, is the cause of illness in the untested cases. The outbreak investigation is ongoing and Canadians will be updated when new information is available.

The risk to Canadians is low. Illnesses can be avoided if oysters are cooked to an internal temperature of 90° Celsius/194° Fahrenheit for a minimum of 90 seconds, and proper hand washing and food safety practices are followed.

Noroviruses are a group of viruses that can cause gastroenteritis in people, an illness that usually includes diarrhea and/or vomiting. Noroviruses are found in the stool or vomit of infected people. They are very contagious and can spread easily from person to person. Some foods can be contaminated at their source. For example, shellfish like oysters may be contaminated by sewage in water before they are harvested.

Investigation Summary

As of March 6, a total of 289 clinical cases of gastrointestinal illness linked to oysters have been reported in three provinces: British Columbia (201), Alberta (40), and Ontario (48). No deaths have been reported. Individuals became sick between December 2016 and February 2017. All individuals who became ill reported having eaten oysters.

The investigation into the cause(s) of the contamination is ongoing and complex. Four shellfish farms where oysters are harvested in British Columbia have been closed for harvest at this time. Investigation into other harvest areas that have been linked to illnesses is ongoing, as gastrointestinal illness linked to consumption of oysters continues to occur. Further information about shellfish farm closures is available through the web links at the end of this notice.

Who is most at risk?

Acute gastrointestinal illnesses such as norovirus illness are common in North America and are very contagious, affecting all age groups. However, pregnant women, people with compromised immune systems, young children and the elderly are at risk for developing more serious complications, like dehydration.

What should you do to protect your health?

The outbreak is ongoing, indicating that contaminated oysters remain on the market (including restaurants and seafood markets and grocery stores). Be aware of the risks associated with consuming raw or undercooked oysters. Food contaminated with noroviruses may look, smell and taste normal. The following safe food handling practices will reduce your risk of getting sick:

Ensure oysters are fully cooked before consuming them. It is recommended to cook oysters to an internal temperature of 90° Celsius (194° Fahrenheit) for a minimum of 90 seconds. Lightly cooking oysters does not kill norovirus.
Discard any oysters that do not open when cooked.
Eat oysters right away after cooking and refrigerate leftovers.
Always keep raw and cooked oysters separate.
Wash your hands well with soap before handling any food. Be sure to wash your hands, cutting boards, counters, knives and other utensils after preparing raw foods.
Noroviruses can be transmitted by ill individuals and are able to survive relatively high levels of chlorine and varying temperatures. Cleaning and disinfecting practices are the key to preventing further illnesses in your home.

Thoroughly clean contaminated surfaces, and disinfect using chlorine bleach, especially after an episode of illness.
After vomiting or diarrhea, immediately remove and wash clothing or linens that may be contaminated with the virus (use hot water and soap).
If you have been diagnosed with norovirus illness or any other gastrointestinal illness, do not prepare food or pour drinks for other people while you have symptoms, and for the first 48 hours after you recover.

Symptoms

People with norovirus illness usually develop symptoms of gastroenteritis within 24 to 48 hours, but symptoms can start as early as 12 hours after exposure. The illness often begins suddenly. Even after having the illness, you can still become re-infected by norovirus.

The main symptoms of norovirus illness are:

diarrhea
vomiting (children usually experience more vomiting than adults)
nausea
stomach cramps
Other symptoms may include:

low-grade fever
headache
chills
muscle aches
fatigue (a general sense of tiredness)
Most people feel better within one or two days, with symptoms resolving on their own, and experience no long-term health effects. As with any illness causing diarrhea or vomiting, people who are ill should drink plenty of liquids to replace lost body fluids and prevent dehydration. In severe cases, patients may need to be hospitalized and given fluids intravenously. If you have severe symptoms of norovirus, consult your healthcare provider.

What the Government of Canada is doing?

The Public Health Agency of Canada is coordinating the response to this outbreak and is in regular contact with its federal and provincial partners to monitor and take collaborative steps to address the outbreak.

The Canadian Food Inspection Agency (CFIA) conducts food safety investigations into the possible food source of an outbreak. CFIA also monitors for biotoxins in shellfish in harvesting areas and is responsible for registering and inspecting fish and shellfish processing plants.

Fisheries and Oceans Canada is responsible for opening and closing shellfish harvest areas, and enforcing closures under the authority of the Fisheries Act and the Management of Contaminated Fishery Regulations.

Under the Canadian Shellfish Sanitation Program (CSSP), Environment and Climate Change Canada monitors pollution sources and sanitary conditions in shellfish growing waters.

The Government of Canada will continue to update Canadians as new information related to this investigation becomes available.